Application of Wavelet Transform to identify motor unit recruitment pattern

Motor unit recruitment pattern represents the time-frequency characteristics of muscle contraction. The Continuous Wavelet Transform (CWT) is a time-frequency signal analysis but its ability to identify motor unit recruitment pattern is still unclear. The purpose of this study was to validate the CWT in identifying the differences in motor unit recruitment pattern, regarding time-space domains, between young and elderly healthy subjects during maximum voluntary knee extension. Ten elderly and 10 young subjects participated in this study. They were asked to perform isometric knee extension at 100% maximum voluntary contraction for 10 seconds. CWT analysis was presented as scalogram. Results showed that the presence of red color spectrum in the young subjects was less than that in the elderly group, indicating that the major recruitments occur more frequently in the elderly. When considering the neuronal firing frequency, the elderly subject operates the firing frequency at a lower range than the young group. The findings in this study confirmed that the CWT can be used to identify the age-related changes in motor unit recruitment pattern.